1. Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a short-wavelength optoelectronic device and a method for fabricating the same.
2. Description of the Related Art
A short-wavelength laser display has been widely used in ultra-density optical recording media, medical instruments, measuring instruments and lithography light sources using deep ultraviolet (DUV). This short-wavelength laser can increase the memory capacity of devices used in the multimedia and information communicating equipments up to tens of times from a few giga byte. Since ultraviolet lasers using the He--Cd gas plasma or frequency modulation manner require large and expensive equipment, these may not be available to the microelectronics.
Compound semiconductors, such as SiC, AlN and GaN, having the wide energy band-gap (WB) have been widely used as short-wavelength optical devices. Finally, blue light-emitting diodes of 400 to 500 nm wavelength have been developed since 1994. Recently, laser diodes having operating time of more than 10,000 hours have been reported. However, DUV semiconductors emitting the wavelength of less than 360 nm have not been yet implemented. The essential reason for this failure is based on the large electric and junction resistance which make the carrier (electrons or holes) injection difficult.
Also, it has been reported that electron-hole pairs (EHPs) are produced by injecting accelerated electrons, which are extracted from field emission devices, into the compound semiconductors, such as SiC, AlN and GaN, and the high emission features are achieved by generating photons through the cathodoluminescence, stimulating the EHPs, inducing the resonance of photons and trapping the photons within the restrict region of an optoelectronic device which has a quantum well and optical reflection films. This manner provides efficient methods in fabricating the optoelectronic devices, such as LED and LD, which generate high energy photons.
The field emission devices emits the electrons through the tunneling effect which is based on the voltage difference between the cathode tip and the grid. As known in the Fowler-Nordheim tunnelling, the electron beam efficiency depends on the work function of the cathode, the diameter of the probe and the voltage difference between the grid and the probe. The generated electrons, which are accelerated at a high energy of a few tens of KeV, are injected into the optoelectronic devices. To increase the emission efficiency, the optoelectronic devices traps the EHPs, which are generated by the hot electrons, within a restricted narrow area. An epitaxial structure made up of the multiple quantum well, which is formed in the WB compound semiconductor, can implement a ultraviolet device together with a micro vacuum electron gun so that it can be used as an optical memory device.
The energy level, which provides the EHPs using the electron beam and provides the recombination, is determined by the multiple quantum wells made from mixed crystal compounds such as (SiC).sub.x (AlN).sub.1-x. However, in the deposition of the mixed crystal compounds using the molecular beam epitaxy and metalorganic CVD methods, the deposition temperature should be higher. Further, since the pressure of nitrogen gas for depositing AlN is very high, it is impossible to obtain an epitaxial film growing method in which each of four elements is evenly distributed on the quadri-mixed crystal compound.
The conventional MBE method using a gas source has a high growing rate of about 1 .mu.m/h by employing the ammonia (NH.sub.3) pyrolysis of high reactivity, but the temperature for the pyrolysis should be higher than 1100.degree. C. Further, this method has a drawback in that the equilibrium gas pressure on the surface of the epitaxial film is high in the nitrogen gas and then results in the deterioration of its quality.
For the purpose of the formation of SiC film, there is provided a method to evaporate a silicon ingot and carbon filament for Si and C, respectively, using the electron beam deposition. The deposition rate is very slow, the sources are frequently replaced with others and then the impurities in the processing chamber deteriorates its quality.
The short in a specific film to be formed can be generated around the high voltage electron beam chamber by means of a film which is previously formed by the repetition and continuous deposition processes. In case where TMAI (tri-methyl aluminum) or ammonia gases, since it is impossible to employ the electron beam deposition equipment which must operate in high vacuum, this method is not economical and not appropriate for the growth of the SiC--AlN super lattice.